Display device with touch sensor, potential control method and program

ABSTRACT

A display device with a touch sensor includes: plural display pixel electrodes; a common electrode arranged opposite to the display pixel electrodes; a display function layer having an image display function; a display control circuit performing image display control so as to fulfill the display function of the display function layer by applying a voltage for display between the display pixel electrodes and the common electrode based on an image signal; and a touch detection electrode provided opposite to the common electrode and forming capacitance between the touch detection electrode and the common electrode, wherein a drive voltage for display applied to the common electrode by the display control circuit is used as a drive signal for the touch sensor, and a gate potential of TFT circuits included in the display pixel electrodes is increased during a period when the drive signal for the touch sensor is applied.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 15/403,897, filed on Jan. 11, 2017, which is acontinuation application of U.S. patent application Ser. No. 14/931,211,filed on Nov. 3, 2015, issued as U.S. Pat. No. 9,575,593 on Feb. 21,2017, which application is a continuation application of U.S. patentapplication Ser. No. 13/675,832, filed on Nov. 13, 2012, issued as U.S.Pat. No. 9,207,481 on Dec. 8, 2015, which application claims priority toJapanese Priority Patent Application JP 2011-255533 filed in the JapanPatent Office on Nov. 22, 2011, the entire content of which is herebyincorporated by reference.

BACKGROUND

The present disclosure relates to a display device with a touch sensor,a potential control method and a program. In particular, the presentdisclosure relates to a display device with a touch sensor, a potentialcontrol method and a program in which sensitivity of the touch sensor isimproved.

In recent years, a display device attracts attention, in which a touchdetection device which is so called a touch panel (hereinafter writtenas a touch sensor) is directly mounted on a liquid crystal display andvarious buttons are displayed on the liquid crystal display to therebyallow information input instead of using normal buttons. The techniqueenables common arrangement of a display and buttons in the tendency ofscreens of mobile devices to increase in size, which brings manyadvantages such as space saving, reduction of the number of components.

However, in the above technique, the thickness of a whole liquid crystalmodule is increased by mounting the touch panel. Particularly, aprotection layer for preventing scratches on the touch panel isnecessary in the application to the mobile devices, therefore, thethickness of the liquid crystal module is increased and thinning isdifficult to be realized.

Accordingly, it is proposed that a common electrode for displayoriginally arranged for a liquid crystal display device is also used asone electrode (drive electrode) of a pair of touch sensor electrodes,and an existing common drive signal as a drive signal for display isalso used as a drive signal for the touch sensor to realize thinning(for example, refer to JP-A-2009-244958 (Patent Document 1)).

SUMMARY

In recent years, devices on which the touch sensor is mounted isincreased, and user needs or user interfaces with respect to the touchsensor become diverse. For example, it is desirable to realizemulti-touch detection detecting a touch with multiple fingers, proximitydetection of a finger (so-called proximity) and detection by anextra-fine point pen. In order to perform the above detection withaccuracy, it is necessary to improve the sensitivity of the touchsensor.

It is necessary to improve S/N (Sensor/Noise) for perform detection withthe extra-fine point pen with accuracy, and it is necessary to furtherimprove S/N for perform the so-called proximity detection. In the casewhere the sensitivity of the touch sensor in Patent Document 1 isincreased, an amplitude of the common drive signal used both as thedrive signal for display and the drive signal for the touch sensor isincreased to thereby realize the increase of sensitivity. When theamplitude (Tx amplitude) of the common drive signal becomes high, theelectric field strength largely changes and the accuracy can beimproved.

On the other hand, a TFT (thin film transistor) used for the liquidcrystal display has a withstand voltage in which reliability can beobtained. If a voltage higher than the standard is applied, the TFT isdestroyed and does not function as a semiconductor device. When thevoltage becomes higher than the withstand voltage in which reliabilityof the TFT can be obtained by increasing the amplitude (Tx amplitude) ofthe common drive signal, the pixel TFT is destroyed, and failure inimages and failure in reliability may occur, therefore, it is difficultto increase the amplitude of the common drive signal. Due to the abovecircumstances, it is also difficult to improve the accuracy of the touchsensor.

In view of the above, it is desirable to improve the accuracy of thetouch sensor.

One embodiment of the present disclosure is directed to a display devicewith a touch sensor including plural display pixel electrodes, a commonelectrode arranged opposite to the display pixel electrodes, a displayfunction layer having an image display function, a display controlcircuit performing image display control so as to fulfill the displayfunction of the display function layer by applying a voltage for displaybetween the display pixel electrodes and the common electrode based onan image signal, and a touch detection electrode provided opposite tothe common electrode and forming capacitance between the touch detectionelectrode and the common electrode, in which a drive voltage for displayapplied to the common electrode by the display control circuit is usedas a drive signal for the touch sensor, and a gate potential of TFTcircuits included in the display pixel electrodes is increased during aperiod when the drive signal for the touch sensor is applied.

The gate potential may be in a high state during a vertical blankingperiod and a horizontal blanking period.

The gate potential may become in the high state in synchronized with thedrive signal for the touch sensor.

The gate potential may become in the high state when writing in apositive polarity display voltage is performed.

The one embodiment of the present disclosure is also directed to apotential control method of a display device with a touch sensorincluding plural display pixel electrodes, a common electrode arrangedopposite to the display pixel electrodes, a display function layerhaving an image display function, a display control circuit performingimage display control so as to fulfill the display function of thedisplay function layer by applying a voltage for display between thedisplay pixel electrodes and the common electrode based on an imagesignal, and a touch detection electrode provided opposite to the commonelectrode and forming capacitance between the touch detection electrodeand the common electrode, the method including using a drive voltage fordisplay applied to the common electrode by the display control circuitas a drive signal for the touch sensor, and increasing a gate potentialof TFT circuits included in the display pixel electrodes is increasedduring a period when the drive signal for the touch sensor is applied.

The one embodiment of the present disclosure is also directed to aprogram for a computer controlling a display device with a touch sensorincluding plural display pixel electrodes, a common electrode arrangedopposite to the display pixel electrodes, a display function layerhaving an image display function, a display control circuit performingimage display control so as to fulfill the display function of thedisplay function layer by applying a voltage for display between thedisplay pixel electrodes and the common electrode based on an imagesignal, and a touch detection electrode provided opposite to the commonelectrode and forming capacitance between the touch detection electrodeand the common electrode, the program allowing the computer to executeprocessing of using a drive voltage for display applied to the commonelectrode by the display control circuit as a drive signal for the touchsensor, and increasing a gate potential of TFT circuits included in thedisplay pixel electrodes is increased during a period when the drivesignal for the touch sensor is applied.

In the display device with the touch sensor, the potential controlmethod and the program according to the one embodiment of the presentdisclosure, plural display pixel electrodes, a common electrode arrangedopposite to the display pixel electrodes, a display function layerhaving an image display function, a display control circuit performingimage display control so as to fulfill the display function of thedisplay function layer by applying a voltage for display between thedisplay pixel electrodes and the common electrode based on an imagesignal, and a touch detection electrode provided opposite to the commonelectrode and forming capacitance between the touch detection electrodeand the common electrode are included. Then, processing of using a drivevoltage for display applied to the common electrode by the displaycontrol circuit as a drive signal for the touch sensor, and increasing agate potential of TFT circuits included in the display pixel electrodesduring a period when the drive signal for the touch sensor is applied isperformed.

Another embodiment of the present disclosure is directed to a displaydevice with a touch sensor including plural display pixel electrodes, acommon electrode arranged opposite to the display pixel electrodes, adisplay function layer having an image display function, a displaycontrol circuit performing image display control so as to fulfill thedisplay function of the display function layer by applying a voltage fordisplay between the display pixel electrodes and the common electrodebased on an image signal, and a touch detection electrode providedopposite to the common electrode and forming capacitance between thetouch detection electrode and the common electrode, in which a drivevoltage for display applied to the common electrode by the displaycontrol circuit is used as a drive signal for the touch sensor, and asignal supplied to gates of TFT circuits included in the display pixelelectrodes is a signal in which different three potentials are switchedat given timings.

The three potentials may include a first potential to be a reference, asecond potential for turning on the TFT circuits and a third potentialat the time of supplying the drive signal for the touch sensor.

A potential of the signal supplied to gates of the TFT circuits in avertical blanking period and in a horizontal blanking period may be thethird potential.

The signal supplied to gates of the TFT circuits may be a signalsynchronized with the drive signal for the touch sensor in which thefirst potential and the third potential are repeated.

The signal supplied to gates of the TFT circuits may be a signal inwhich different three potentials are switched at given timings whenwriting in a positive polarity display voltage is performed, and is asignal in which two potentials of the different three potentials areswitched at given timings when writing in a negative polarity displayvoltage is performed.

The another embodiment of the present disclosure is also directed to apotential control method of a display device with a touch sensorincluding plural display pixel electrodes, a common electrode arrangedopposite to the display pixel electrodes, a display function layerhaving an image display function, a display control circuit performingimage display control so as to fulfill the display function of thedisplay function layer by applying a voltage for display between thedisplay pixel electrodes and the common electrode based on an imagesignal, and a touch detection electrode provided opposite to the commonelectrode and forming capacitance between the touch detection electrodeand the common electrode, the method including using a drive voltage fordisplay applied to the common electrode by the display control circuitas a drive signal for the touch sensor, and allowing a signal suppliedto gates of TFT circuits included in the display pixel electrodes to bea signal in which different three potentials are switched at giventimings.

The another embodiment of the present disclosure is also directed to aprogram for a computer controlling a display device with a touch sensorincluding plural display pixel electrodes, a common electrode arrangedopposite to the display pixel electrodes, a display function layerhaving an image display function, a display control circuit performingimage display control so as to fulfill the display function of thedisplay function layer by applying a voltage for display between thedisplay pixel electrodes and the common electrode based on an imagesignal, and a touch detection electrode provided opposite to the commonelectrode and forming capacitance between the touch detection electrodeand the common electrode, the program allowing the computer to executeprocessing of using a drive voltage for display applied to the commonelectrode by the display control circuit as a drive signal for the touchsensor, and allowing a signal supplied to gates of TFT circuits includedin the display pixel electrodes to be a signal in which different threepotentials are switched at given timings.

In the display device with the touch sensor, the potential controlmethod and the program according to the another embodiment of thepresent disclosure, plural display pixel electrodes, a common electrodearranged opposite to the display pixel electrodes, a display functionlayer having an image display function, a display control circuitperforming image display control so as to fulfill the display functionof the display function layer by applying a voltage for display betweenthe display pixel electrodes and the common electrode based on an imagesignal, and a touch detection electrode provided opposite to the commonelectrode and forming capacitance between the touch detection electrodeand the common electrode are included. Then, processing of using a drivevoltage for display applied to the common electrode by the displaycontrol circuit as a drive signal for the touch sensor, and allowing asignal supplied to gates of TFT circuits included in the display pixelelectrodes to be a signal in which different three potentials areswitched at given timings is performed.

According to the embodiments of the present disclosure, the accuracy ofthe touch sensor can be improved.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A and 1B are diagrams for explaining operation principle of adisplay device with a touch sensor to which the present disclosure isapplied, showing a non-contact state of a finger;

FIGS. 2A and 2B are diagrams for explaining operation principle of thedisplay device with the touch sensor, showing a contact state of afinger;

FIGS. 3A and 3B are diagrams for explaining operation principle of thedisplay device with the touch sensor, showing waveform examples of adrive signal and a detection signal of the touch sensor;

FIG. 4 is a cross-sectional view showing a schematic cross-sectionalstructure of the display device with the touch sensor;

FIG. 5 is a perspective view showing a structure example of a relevantpart (a common electrode and a sensor detection electrode) of thedisplay device with the touch sensor;

FIG. 6 is a configuration example of a pixel;

FIGS. 7A and 7B are diagrams showing the relation of potentials in apositive polarity and a negative polarity;

FIGS. 8A and 8B are diagrams showing the relation of potentials in thepositive polarity and the negative polarity;

FIGS. 9A and 9B are diagrams for explaining arrangement of gate lines;

FIG. 10 is a diagram for explaining arrangement of gate lines;

FIGS. 11A and 11B are diagrams indicating configuration examples of gatebuffers;

FIG. 12 shows timing charts for explaining the relation of potentials ina blanking period;

FIG. 13 shows timing charts for explaining the relation of potentials inthe blanking period;

FIG. 14 shows timing charts for explaining the relation of potentials inthe blanking period;

FIG. 15 shows timing charts for explaining the relation of potentials inthe blanking period;

FIG. 16 shows timing charts for explaining the relation of potentials inthe blanking period; and

FIG. 17 is a diagram for explaining recording media.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be explainedwith reference to the drawings.

The present disclosure can be applied to a device in which a commonelectrode for display arranged for a liquid crystal display device isalso used as one electrode (drive electrode) of a pair of touch sensorelectrodes, and an existing common drive signal as a drive signal fordisplay is also used as a drive signal for the touch sensor to realizethinning. Such display will be explained first.

[Display Device with Touch Sensor]

The basic principle of a touch detection system in a display device witha touch sensor according to an embodiment is shown with reference toFIGS. 1A and 1B to FIGS. 3A and 3B. The touch detection system isembodied as a capacitance-type touch sensor, in which a pair ofelectrodes (a drive electrode E1 and a detection electrode E2) arrangedopposite to each other so as to sandwich a dielectric D are used to forma capacitor device as shown in FIG. 1A.

The structure is represented as an equivalent circuit shown in FIG. 1B.The drive electrode E1, the detection electrode E2 and the dielectric Dform a capacitor device C1. One terminal of the capacitor device C1 isconnected to an AC signal source S and the other terminal P is groundedthrough a resistance R as well as connected to a voltage detector DET.When an AC rectangular wave Sg (FIG. 3B) having a predeterminedfrequency (for example, approximately several kHz to several dozen kHz)is applied from the AC signal source S to the drive electrode E1 (oneterminal of the capacitor C1), an output waveform (a detection signalVdet) as shown in FIG. 3A appears at the detection electrode E2 (theother terminal P of the capacitor device C1). The AC rectangular wave Sgcorresponds to a later-described common drive signal Vcom.

In a state where a finger does not touch the sensor, a current I0corresponding to a capacitance value of the capacitor device C1 flows inaccordance with charge/discharge with respect to the capacitor device C1as shown in FIG. 1B. A potential waveform at the other terminal P of thecapacitor device C1 at this time is, for example, as shown by a waveformV0 of FIG. 3A, which is detected by the voltage detector DET.

On the other hand, in a state where a touch touches the sensor, acapacitor device C2 formed by the finger is added in series to thecapacitor device C1 as shown in FIGS. 2A and 2B. In this state, currentsI1 and I2 respectively flow in accordance with charge/discharge withrespect to the capacitor devices C1 and C2. A potential waveform at theother terminal P of the capacitor device C1 at this time is, forexample, as shown by a waveform V1 of FIG. 3A, which is detected by thevoltage detector DET. At this time, a potential at a point P will be adivided potential determined by values of the currents I1 and I2 flowingthrough the capacitor devices C1 and C2.

Accordingly, the waveform V1 has a lower value than the waveform V0 inthe non-contact state. The voltage detector DET compares a detectedvoltage with a given threshold voltage Vth, determining the state as thenon-contact state when the voltage is lower than the threshold voltage,and determining the state as the contact state when the voltage ishigher than the threshold voltage as described later. The touchdetection can be performed as described above.

FIG. 4 shows a cross-sectional structure of a relevant part of thedisplay device with the touch sensor. The display device with the touchsensor uses a liquid crystal display device as a display device as wellas part of electrodes (a later-described common electrode 43) originallyarranged for the liquid crystal device and the a drive signal fordisplay (a later-described common drive signal Vcom) are also used asanother electrode and another signal, thereby forming thecapacitance-type touch sensor.

As shown in FIG. 4, the display device with the touch sensor includes apixel substrate 2, a counter substrate 4 arranged opposite to the pixelsubstrate 2 and a liquid crystal layer 6 inserted between the pixelsubstrate 2 and the counter substrate 4. The pixel substrate 2 includesa TFT substrate 21 as a circuit substrate and plural pixel electrodes 22arranged on the TFT substrate 21 in a matrix state. On the TFT substrate21, not-shown display drivers for driving respective pixel electrodes 22and TFTs (thin-film transistors) as well as wiring lines such as sourcelines for supplying pixel signals to respective pixel electrodes, gatelines for driving respective TFTs are formed.

The counter substrate 4 includes a glass substrate 41, a color filter 42formed on one face of the glass substrate 41 and a common electrode 43formed on the color filter 42. The color filter 42 is formed bycyclically arranging color filter layers of three colors, which are, forexample, red (R), green (G) and blue (B), in which three colors of R, Gand B are associated with each display pixel (pixel electrode 22) as oneset. The common electrode 43 is also used as a sensor drive electrodeforming part of the touch sensor performing a touch detection operation,which corresponds to the drive electrode E1 in FIG. 1A.

The common electrode 43 is connected to the TFT substrate 21 by acontact conductive column 7. The common drive signal Vcom having an ACrectangular wave is applied from the TFT substrate 21 to the commonelectrode 43 through the contact conductive column 7. The common drivesignal Vcom is for fixing display voltages of respective pixels withpixel voltages applied to the pixel electrodes 22, which is also used asthe drive signal for the touch sensor and corresponds to the ACrectangular wave Sg supplied from the drive signal source S of FIG. 1B.

On the other face of the glass substrate 41, a sensor detectionelectrode 44 is formed, and a polarizing plate 45 is further arranged onthe sensor detection electrode 44. The sensor detection electrode 44forms part of the touch sensor, which corresponds to the detectionelectrode E2 in FIG. 1A.

The liquid crystal layer 6 modulates light transmitting through thelayer in accordance with an electric field state, and various modes ofliquid crystal such as TN (twisted nematic), VA (vertical alignment) andECB (Electrically Controlled Birefringece) can be used.

Alignment films are respectively arranged between the liquid crystallayer 6 and the pixel substrate 2 as well as between the liquid crystallayer 6 and the counter substrate 4, and an incident-side polarizingplate is arranged under the pixel substrate 2, which are not shown here.

FIG. 5 perspectively shows a structure example of the common electrode43 and the sensor detection electrode 44 in the counter substrate 4. Inthe example, the common electrode 43 is divided to have a strip-shapedelectrode pattern including plural electrodes extending in a right andleft direction in the drawing. The common drive signal Vcom issequentially supplied to respective electrodes in the pattern, andline-sequential scanning drive is performed in a time sharing manner bya driver 43D.

On the other hand, the sensor detection electrode 44 has a strip-shapedelectrode pattern including plural electrodes extending in a directionorthogonal to the extending direction of the electrode pattern of thecommon electrode 43. Detection signals Vdet are outputted fromrespective electrodes in the pattern of the sensor detection electrode44, which are inputted to a detection circuit (not shown).

Next, an operation of the display device with the touch sensor havingthe above structure will be explained. A display driver (not shown) ofthe pixel substrate 2 supplies the common drive signal Vcom in aline-sequential manner to respective electrodes in the pattern of thecommon electrode 43. The display driver also supplies pixel signals tothe pixel electrodes 22 through the source lines as well as controlsswitching of the TFTs of respective pixel electrodes through gate linesin the line-sequential manner so as to be synchronized with the supplyof pixel signals. Accordingly, the electric field in a verticaldirection (a direction vertical to the substrate) fixed by the commondrive signal Vcom and respective pixel signals is applied to respectivepixels in the liquid crystal layer 6 to modulate the liquid crystalstate. The display by so-called inversion driving is performed in theabove manner.

On the other hand, the capacitor devices C1 are formed at intersectionsbetween respective electrodes in the pattern of the common electrode 43and respective electrodes in the pattern of the sensor detectionelectrode 44 in the counter substrate 4. When the common drive signalVcom is sequentially applied to respective electrodes in the pattern ofthe common electrode 43, charge/discharge is performed with respect torespective capacitor devices C1 in one column formed at intersectionsbetween the applied respective electrodes in the pattern of the commonelectrode 43 and respective electrodes in the pattern of the sensordetection electrode 44. As a result, the detection signals Vdet havingsizes corresponding to capacitance values of the capacitor devices C1are respectively outputted from respective electrodes in the pattern ofthe sensor detection electrode 44. In the state where a user's fingerdoes not touch the surface of the counter substrate 4, the sizes of thedetection signal Vdet are approximately the same. The column of thecapacitor devices C1 to be charged/discharged will be moved in theline-sequential manner with the scanning by the common drive signalVcom.

Here, when a user's finger touches any position on the surface of thecounter substrate 4, the capacitor device C2 formed by the finger isadded to the capacitor device C1 originally formed on the touchposition. As a result, a value of the detection signal Vdet at a pointwhere the touch position has been scanned (namely, when the common drivesignal Vcom is applied to an electrode in the pattern corresponding tothe touch position in the electrode pattern of the common electrode 43)becomes lower than values at other positions. The detection circuitcompares the detection signal Vdet with the threshold voltage Vth anddetermines the position as the touch position when the detected signalVdet is lower than the threshold voltage Vth. The touch position can becalculated from a timing when the common drive signal Vcom is appliedand a timing when the detection signal Vdet lower than the thresholdvoltage Vth is detected.

As described above, the capacitance-type touch sensor is configured sothat the common electrode 43 originally provided in the liquid crystaldisplay device is also used as one of a pair of touch sensor electrodesincluding the drive electrode and the detection electrode as well as thecommon drive signal Vcom as the drive signal for display is also used asthe drive signal for the touch sensor in the present embodiment,therefore, only the sensor detection electrode 44 has to be newlyprovided and it is not necessary to newly prepare the drive signal forthe touch sensor.

The structure can be simplified by applying the above structure. Thesensor detection electrode 44 is divided into plural electrodes in thepattern to be individually driven in a time sharing manner, therefore,the detection of the touch position can be performed.

The active-matrix liquid crystal display functioning as a display of thetouch sensor display device shown in FIG. 4 and FIG. 5 as describedabove includes scanning (gate) lines arranged in rows, signal linesarranged in columns and pixels arranged in the matrix state so as tocorrespond to intersections between respective scanning lines and signallines. The liquid crystal display also includes a horizontal drivecircuit allowing devices in a row to be active in each one horizontalperiod (1H) and a vertical drive circuit selecting and driving pixelsrow by row (line by line) by sequentially scanning the scanning lines ofthe rows in the active state.

Then, a video signal for each horizontal period is written into pixelsof each selected row, and the video signal for one frame (or one field)is held. The display device functions in this manner as well asfunctions as the touch panel as described above.

As described above, the common electrode 43 originally provided in theliquid crystal display device is also used as one of a pair of touchsensor electrodes including the drive electrode and the detectionelectrode and the common drive signal Vcom as the drive signal fordisplay is also used as the drive signal for the touch sensor,therefore, the size of an amplitude of the common drive signal Vcom haveto satisfy conditions explained below.

[Withstand Voltage]

FIG. 6 is a block diagram showing a detailed configuration of one pixel(liquid crystal display device). The liquid crystal display deviceincludes a TFT circuit 61 and a liquid crystal capacitor 62. A gateelectrode of the TFT circuit 61 is connected to a gate line, a sourceelectrode (or a signal electrode) of the TFT circuit 61 is connected toa signal line and a drain electrode of the TFT circuit 61 is connectedto the liquid crystal capacitor 62. The common drive signal Vcom isapplied to a counter electrode (electrode not being connected to the TFTcircuit 61) of the liquid crystal capacitor 62.

The TFT circuit 61 drives the liquid crystal capacitor 62 by applying avoltage to the liquid crystal capacitor 62. That is, the TFT circuit 61drives the liquid crystal capacitor 62 based on a signal voltageobtained when a corresponding gate signal is ON.

A lifetime of liquid crystal is reduced when a DC voltage is applied.Accordingly, in a common liquid crystal display, the voltage to beapplied to the pixel electrode of the liquid crystal capacitor 62 ischanged between the positive-voltage side and the negative-voltage sideat regular intervals based on the voltage to be applied to the commonelectrode to thereby prevent the reduction of lifetime of liquidcrystal.

As described later, a gate negative supply is changed on thepositive-voltage side (hereinafter referred to as a positive polarity)and the negative-voltage side (hereinafter referred to as a negativepolarity) in the present embodiment. Accordingly, the amplitude of thecommon drive signal Vcom can be increased for improving the accuracy ofthe touch sensor while controlling the TFT circuit not to be damaged.

As the TFT circuit 61 has the withstand voltage in which reliability canbe obtained. If a voltage higher than the standard is applied, the TFTis damaged and it is difficult that the TFT functions as thesemiconductor device. On the other hand, when the amplitude (Txamplitude) of the common drive signal Vcom becomes high, the electricfield strength largely changes and the sensitivity of the touch sensorcan be improved.

User needs or user interfaces with respect to the touch sensor becomediverse, for example, it is desirable to realize multi-touch detectiondetecting a touch with multiple fingers, so-called proximity detectionof a finger and detection by an extra-fine point pen. In order toperform the above detection with accuracy, it is necessary to improvethe sensitivity of the touch sensor, and it is necessary to increase theamplitude (Tx amplitude) of the common drive signal Vcom for improvingthe sensitivity.

However, when the amplitude of the common drive signal Vcom is simplyincreased, there is a possibility that the voltage exceeds the withstandvoltage of the TFT circuit 61. A potential difference Vgd between a gatepotential Vg and a drain potential (pixel potential) Vd of the TFTcircuit 61 can be calculated by the following expressions from apotential Vpix of the liquid crystal capacitor 62, a potential Vcom ofthe amplitude of the common drive signal Vcom and a potential Gate of apower supply of the gate.

Potential difference Vgd=potential Vpix+potential Vcom−potential Gate

For example, assume that a potential of the withstand voltage of the TFTcircuit 61 is 7, the potential Vpix=1, the potential Vcom=2 and thepotential Gate=−3. In this case, the potential difference Vgd will be 6from the above expression. When the potential difference Vgd is 6, theTFT circuit 61 operates within a range of the withstand voltage in whichreliability can be obtained as the value is lower than 7 as thewithstand voltage.

However, the amplitude of the common drive signal Vcom is increased forimproving the sensitivity of the touch sensor so that the potential Vcomis doubled to be 4, the potential difference Vgd will be 8. When thepotential difference Vgd is 8, the TFT circuit 61 operates outside therange of the withstand voltage in which reliability can be obtained asthe value is higher than 7 as the withstand voltage, which may causedamage and so on. Accordingly, it is difficult to set the amplitude ofthe common drive signal Vcom to such potential.

Further explanation will be made concerning the above. The pixel hasboth polarities of the negative polarity and the positive polarity asdescribed above. When the pixel has the positive polarity, the voltagemay exceed the withstand voltage of the TFT circuit 61 at the time ofincreasing the amplitude of the common drive signal Vcom. This will beexplained with reference to FIGS. 7A and 7B.

FIG. 7A is a diagram showing the relation of potentials at the time ofthe negative polarity, and FIG. 7B is a diagram showing the relation ofpotentials at the time of the positive polarity. In FIGS. 7A and 7B, thepotential Gate applied to the gate of the TFT circuit 61 is representedby solid lines, the potential Vcom of the common drive signal Vcom isrepresented by dotted lines and the potential Vpix applied to the liquidcrystal capacitor 62 is represented by dashed lines.

Referring to FIG. 7A, when the TFT circuit 61 is turned on by changingthe gate signal of the TFT circuit 61 from a potential GateA to apotential GateB, the potential Vpix in the negative voltage is appliedin the case of the negative polarity. The potential GateA is a referencepotential and the potential GateB is a potential necessary for turningon the TFT circuit 61. When the potential Vpix to be applied is VpixA,the relation between the potential GateB and the potential VpixA is asshown in FIG. 7A.

When a potential VcomB of the common drive signal Vcom is applied in thecase where the potential of the liquid crystal capacitor 62 is thepotential VpixA, the potential of the liquid crystal capacitor 62 isaccordingly increased to be the potential VpixB. At this time, thepotential difference between the potential VpixB and the potentialGateA, namely, the potential difference Vgd is within the range ofwithstand voltage. Accordingly, the TFT circuit 61 is not damaged.

Referring to FIG. 7B, when the TFT circuit 61 is turned on by changingthe gate signal of the TFT circuit 61 from the potential GateA to thepotential GateB, the potential Vpix in the positive voltage is appliedin the case of the positive polarity. When the potential Vpix to beapplied is VpixC, the relation between the potential GateB and thepotential VpixC is as shown in FIG. 7B.

When the potential VcomB of the common drive signal Vcom is applied inthe case where the potential of the liquid crystal capacitor 62 is thepotential VpixC, the potential of the liquid crystal capacitor 62 isaccordingly increased to be the potential VpixD. Even when the potentialVcomB is the same potential as in the case of the negative polarity, thepotential of the liquid crystal capacitor 62 varies to be a higherpotential VpixD than the potential in the case of the negative polarity.The potential difference between the potential VpixD and the potentialGateA, namely, the potential difference Vgd is higher than the case ofthe negative polarity and may be outside the range of the withstandvoltage. Accordingly, damage and the like occur in the TFT circuit 61,which is not preferable.

As described above, the voltage may exceed the withstand voltage of theTFT circuit 61 in the case of the positive polarity by increasing theamplitude of the common drive signal Vcom is increased even when the TFTcircuit 61 is designed to operate within the range of the withstandvoltage in the negative polarity, therefore, it is difficult to increasethe amplitude of the common drive signal Vcom. Accordingly, as shown inFIGS. 8A and 8B, the potential Gate applied to the gate of the TFTcircuit 61 is switched at the time of the positive polarity and at thetime of negative polarity, thereby increasing the amplitude of thecommon drive signal Vcom without exceeding the withstand voltage of theTFT circuit 61.

The relation of potentials in the negative polarity shown in FIG. 8A isthe same as the relation of potentials in the negative polarity shown inFIG. 7A. That is, the potential Gate applied to the gate of the TFTcircuit 61 in the negative polarity varies as shown below.

Potential GateA→Potential GateB→Potential GateA

As shown above, the signal in which two potential are switched is usedin the negative polarity.

The relation of potentials in the positive polarity is as shown in FIG.8B. Also in the case shown in FIG. 8B, the common drive signal Vcom andthe potential VpixC are applied to the TFT circuit 61 in the same manneras in the case shown in FIG. 7B. However, the potential Gate applied tothe gate of the TFT circuit 61 varies as shown below, which is differentfrom the case shown in FIG. 7B.

Potential GateA→Potential GateB→Potential GateC

Though not shown in FIG. 8B, the potential is returned to the potentialGateA after a given period of time passes from the potential GateC. Notethat “after the given period of time passes” depends on whether thepotential is changed corresponding the amplitude of the common drivesignal Vcom or the potential is not changed during variation of theamplitude of the common drive signal Vcom as described later.

In the positive polarity, the TFT circuit 61 is turned on by changingthe gate signal of the TFT circuit 61 from the potential GateA to thepotential GateB, after that, the potential is not returned to thepotential GateA but the potential falls to the potential GateC which ishigher than the potential GateA and lower than the potential GateB fromthe potential GateA. In particular, the potential falls to the potentialGateA once from the GateB, then, rises to the potential GateC when thecircuit operates as the touch sensor as shown in FIG. 8B.

In the positive polarity, The potential VpixC of the positive voltage isapplied to the TFT circuit 61. When the potential VcomB is applied bythe common drive signal Vcom in the case where the potential of theliquid crystal capacitor 62 is the potential VpixC, the potential of theliquid crystal capacitor 62 is increased accordingly to be the potentialVpixD. At this time, there is a possibility that the potentialdifference Vgd between the potential VpixD and the potential Gate A(potential difference VgdDA) is outside the range of the withstandvoltage in the example shown in FIG. 7B, however, the potentialdifference Vgd between the potential VpixD and the potential GateC(potential difference VgdDC) will be a value lower than the potentialdifference VgdDA in the example shown in FIG. 8B, which can be withinthe range of the withstand voltage.

As described above, the potential GateC is set to a potential in whichthe potential VgdDC falls within the range of the withstand voltage.When the potential VgdDC falls within the range of the withstand voltageby setting the potential GateC, the amplitude of the common drive signalVcom can be increased and the accuracy of the touch sensor can beimproved.

As described above, the signal voltage in which two potentialsalternately appear is applied to the gate of the TFT circuit 61 at thetime of the negative polarity, and the signal voltage in which threepotentials appear is applied to the gate of the TFT circuit 61 at thetime of the positive polarity. In other words, the gate negative supplyis allowed to be independent in the negative polarity and in thepositive polarity, and the potential of the gate negative supply isincreased in the positive polarity pixel, thereby securing the withstandvoltage.

As described later, it is possible to configure the device so that thesignal voltage in which three potentials appear is applied to the gateof the TFT circuit 61 also at the time of the negative polarity,however, it is necessary, for configuring the device, that the switchingtiming of potentials of the signal in which three potentials appearsatisfies given conditions. The conditions and so on will be describedlater. First, the case where the gate negative supply is allowed to beindependent in the negative polarity and in the positive polarity, andthe signal voltage in which two potentials appear alternately is appliedto the gate of the TFT circuit 61 at the time of the negative polarityand the signal voltage in which three potential appear is applied to thegate of the TFT circuit 61 at the time of the positive polarity will becontinuously explained.

Hereinafter, arrangements of pixels and configurations of gate buffersin the case where the gate negative supply is independent in thenegative polarity and the positive polarity will be explained. Theexplanation will be made while comparing the case where the gatenegative supply is independent with the case where the gate negativesupply is not independent in the negative polarity and the positivepolarity explained with reference to FIGS. 7A and 7B.

[Polarity Arrangement Pattern of Pixels]

FIGS. 9A and 9B are views for explaining a polarity arrangement patternof pixels and a connection pattern of gate lines. FIG. 9A shows a casewhere the same gate signal is used for the negative polarity and thepositive polarity as explained with reference to FIGS. 7A and 7B, andFIG. 9B shows a case where different gate signals are used for thenegative polarity and the positive polarity as explained with referenceto FIGS. 8A and 8B. The polarity arrangement pattern shown in FIGS. 9Aand 9B is called a dot inversion drive, which is a pattern in whichpositive polarity pixels and negative polarity pixels are arranged in azigzag pattern.

In the dot inversion drive, for example, negative polarity pixels arearranged in up, down, right and left directions of a positive polaritypixel at an arbitrary position, and similarly, positive polarity pixelsare arranged at up, down, right and left directions of a negativepolarity pixel. As shown in FIG. 9A, when the same gate signal is usedfor the negative polarity and the positive polarity, the same gatesignal is supplied to pixels of both the negative polarity and thepositive polarity.

Accordingly, for example, a gate line 101-1 is connected to respectivepixels of both the negative polarity and the positive polarity arrangedin a single horizontal row on an upper side in the drawing for supplyingthe gate signal. Similarly, a gate line 101-2 is connected to respectivepixels of both the negative polarity and the positive polarity arrangedin the second horizontal row from the top in the drawing for supplyingthe gate signal.

As described above, when the same gate signal is used for the negativepolarity and the positive polarity, gate lines are connected independentof pixels of the negative polarity and the positive polarity.

On the other hand, as shown in FIG. 9B, when the different gate signalsare used for the negative polarity and the positive polarity, differentgate signals are supplied to the negative polarity pixels and thepositive polarity pixels. Accordingly, for example, a gate line 111-2 isconnected to respective pixels of the positive polarity in pixelsarranged in the single horizontal row on the upper side in the drawingand respective pixels of the positive polarity in pixels arranged in thesecond horizontal row from the top for supplying the gate signal.

Similarly, a gate line 111-3 is connected to respective negativepolarity pixels in pixels arranged in the second horizontal row from thetop and respective negative polarity pixels in pixels arranged in thethird horizontal row from the top for supplying the gate signal.

As described above, when different gate signals are used for thenegative polarity and the positive polarity, pixels of the same polarityare connected to the same gate line. In the example shown in FIG. 9B,the case where pixels of the same polarity positioned adjacent to eachother in the vertical direction are connected to the same gate line isshown, however, the embodiment is not limited to the example. Theembodiment can be applied to any structure in which pixels of the samepolarity are connected to the same gate line. For example, theembodiment can be applied not only to the dot inversion drive method asshown in FIGS. 9A and 9B but also to a line inversion drive method shownin FIG. 10.

In the line inversion drive method, for example, pixels of the samepositive polarity are arranged in a right and left direction of apositive polarity pixel at an arbitrary position, and similarly, pixelsof the same negative polarity are arranged in the right and leftdirection of a negative pixel. That is, positive pixels or negativepixels are arranged in the whole one line, and the positive polarity andthe negative polarity are alternately arranged row by row. As shown inFIG. 10, pixels of the negative polarity or the positive polarity arearranged in each line, therefore, the same gate signal is used in oneline.

Accordingly, for example, a gate line 121-1 is connected to respectivepixels of the positive polarity arranged in a single horizontal row onan upper side in the drawing for supplying the gate signal. Similarly, agate line 121-2 is connected to respective pixels of the negativepolarity arranged in the second horizontal row from the top in thedrawing for supplying the gate signal.

As described above, when different gate signals are used for thenegative polarity and the positive polarity, the pixels of the samepolarity are connected to the same gate line.

[Configurations of Gate Buffers]

FIGS. 11A and 11B are diagrams showing configurations of gate buffers.FIG. 11A shows a configuration of gate buffers used when the gate linesand pixels are connected as shown in FIG. 9A and the same gate signal isused for the negative polarity and the positive polarity, and FIG. 11Bshows a configuration of gate buffers used when the gate lines and thepixels are connected as shown in FIG. 9B and the different gate signalsare used for the negative polarity and the positive polarity.

Referring to FIG. 11A, a buffer 151 and a buffer 152 are respectivelyconnected to a VGL line outputting a signal in a potential correspondingto the potential GateA and a VGH line outputting a signal in a potentialcorresponding to the potential GateB. The buffer 151 and the buffer 152switch the signal supplied from the VGL line and the signal suppliedfrom VGH line at given timings respectively based on respectiveinstructions from the outside which are not shown, supplying the signalto connected gate lines.

The buffer 151 is connected to a gate line (n) and the buffer 152 isconnected to a gate line (n+1). For example, when the buffer 151 isconnected to the gate line 101-1 (FIG. 9A), the buffer 152 is connectedto the gate line 101-2 (FIG. 9A). Though the two buffers are shown inFIG. 11A, buffers corresponding to the number of the gate lines areprovided.

When different gate signals are used for the negative polarity and thepositive polarity with respect to the configuration of buffers, aconfiguration of gate buffers will be as shown in FIG. 11B. In theconfiguration of gate buffers shown in FIG. 11B, two buffers which are abuffer 161 and a buffer 162 are shown in the same manner as theconfiguration of gate buffers shown in FIG. 11A, however, bufferscorresponding to the number of gate lines are provided. The two buffersof them are shown for explanation.

The buffer 161 and the buffer 162 are the same as the case of the buffer151 and the buffer 152 shown in FIG. 11A in a point that the buffer 161and the buffer 162 are respectively connected to the VGH line outputtingthe signal in the potential corresponding to the potential GateB.However, the buffer 161 and the buffer 162 differs from the buffer 151and the buffer 152 shown in FIG. 11A in a point that the buffer 161 andthe buffer 162 are connected to two VGL lines, that is, the buffer 161is connected to a VGL1 line outputting a signal in a potentialcorresponding to the potential GateA through a switch 171 and the buffer162 is connected to a VLG2 line outputting a signal in a potentialcorresponding the potential GateC through a switch 172.

The buffer 161 and the buffer 162 switch the signal supplied from theVGL1 line or the VGL2 line and the signal supplied from the VGH line atgiven timings based on respective instructions from the outside whichare not shown, supplying the signal to connected gate lines. The switch171 and the switch 172 also switch the connection of the VGL1 line andthe VGL2 at given timings based on respective instructions from theoutside which are not shown, supplying the signal supplied from the VGL1line or the VGL2 line to the buffer 161 and the buffer 162 respectively.

The buffer 161 is connected to the gate line (n) and the buffer 162 isconnected to the gate line (n+1). For example, when the buffer 161 isconnected to the gate line 111-2 (FIG. 9B), the buffer 162 is connectedto the gate line 111-3 (FIG. 9B).

For example, when the switch 171 is connected to a terminal “a”, thesignal in the potential corresponding to the potential GateC is ready tobe supplied from the VGL2 line to the buffer 161. The potential GateC isa signal voltage supplied to pixels of the positive polarity. The signalin the potential corresponding to the potential GateC is outputted tothe gate line connected from the buffer 161 at a timing when the TFTcircuits 61 of pixels of the positive polarity are turned on.

At this time, the switch 172 is connected to a terminal “d” and thesignal in the potential corresponding to the potential GateA is ready tobe supplied from the VGL1 line to the buffer 161. The potential GateA isthe signal voltage supplied to the negative polarity pixels or thesignal voltage supplied to the positive polarity pixels when the devicedoes not function as the touch sensor of the positive polarity pixels.The signal in the potential corresponding to the potential GateA isoutputted to the gate line connected from the buffer 161 at a timingwhen the TFT circuits 61 of pixels of the negative polarity or thepositive polarity are turned on.

As describe above, the potential of the negative supply applied to thegate can be changed at the time of the negative polarity and at the timeof the positive polarity by providing switches to switch the VGL lines.It is also possible to prevent the voltage from exceeding the withstandvoltage of the TFT circuit 61, thereby allowing the TFT circuit 61 tooperate within the range in which reliability can be kept. Additionally,the amplitude of the common drive signal Vcom can be increased within arange in which the voltage does not exceed the withstand voltage of theTFT circuit 61, therefore, the accuracy of the touch sensor can beimproved.

[Explanation with Reference to Timing Charts]

Furthermore, to secure the withstand voltage of the TFT circuit 61 byincreasing the potential of the gate negative supply of pixels of thepositive polarity when the device functions as the touch sensor will beexplained with reference to timing charts.

As described above, writing performed when the display device with thetouch sensor functions as the display device includes writing on thepositive polarity side and the negative polarity side to perform ACinversion driving so that deviation of charges does not occur. Thepotential difference Vgd will be highest when the pixel TFT (TFT circuit61) is in a period of holding the pixel potential in which positivepolarity writing is performed. Accordingly, explanation has been madethat the amplitude of the common drive signal Vcom can be increased bycontrolling the gate potential of the pixel TFT to have the potential(potential GateC) in which the potential difference Vgd does not exceedthe given standard as well as the pixel potential does not leak withrespect to the pixel in which the positive polarity writing side hasbeen performed.

At this time, the potential is controlled to be the above potentialGateC for allowing the device to function as the touch sensor in avertical blanking period (V blank) and a horizontal blanking period (Hblank) which are periods of time when writing is not performed, therebycontrolling the potential so that leakage due to image data does notoccur. It is desirable that a Sig-potential is a fixed potential inwhich leakage does not occur.

The display device with the touch sensor functions as the touch sensorby using the vertical blanking period and the horizontal blankingperiod. The control of increasing the potential of the gate negativesupply of the polarity pixels is performed in the vertical blankingperiod and the horizontal blanking period respectively. FIG. 12 showstiming charts in the vertical blanking period.

Referring to FIG. 12, VCK represents a vertical synchronization signaland Sig represent a video signal. Vcom, Gate1 to GateN and Vpix1 toVpixN respectively represent the potential Vcom, the potentials Gate andthe potentials Vpix. Moreover, Gate 1 to Gate N respectively representpotentials of output signals from buffers connected to gate lines 1 toN, and Vpix1 to VpixN respectively represent potentials of the liquidcrystal capacitors C connected to the gate lines 1 to N. Also, Vcom,Gate1 to GateN, and Vpix1 to VpixN satisfy the relation of potentialsexplained with reference to FIGS. 8A and 8B.

The common drive signal Vcom is a signal with a given cycle during thevertical blanking period, in which the potential VcomA and the potentialVcomB are repeated, sequentially supplied to respective pixels. Assumethat the Gate1 is a potential of the gate line 1 connected to thepositive polarity pixels. In this case, the positive polarity pixelsconnected to the gate line 1 are turned on when the potential GateA isswitched to the potential GateB at a timing shown in FIG. 12, andwriting is performed based on the video signal. The potential Vpix1 ismaintained in the potential VpixC after the writing is performed.

When the vertical blanking period starts and the common drive signalVcom in which the potential VcomA and the potential VcomB are repeatedwith a given cycle is added while the potential Vpix1 of the liquidcrystal capacitor C is maintained in the potential VpixC, the potentialVpix1 of the liquid crystal capacitor C becomes a signal in which thepotential VpixC and the potential VpixD are repeated so as to correspondto the cycle. As the potential Vpix1 of the liquid crystal capacitor Cof the positive polarity pixels varies as described above, the potentialof Gate1 is fixed to the potential GateC during the period. That is, thepotential of Gate1 is fixed to the potential GateC during the blankingperiod as shown in FIG. 12.

As described above, the potential of Gate1 is fixed to the potentialGateC during the blanking period at the time of the positive polarity,therefore, it is possible to control the voltage not to exceed thewithstand voltage of the TFT circuit 61 even when the potential Vpix 1of the liquid crystal capacitor C varies between the potential VpixC andthe potential VpixD as explained with reference to FIG. 8B.Additionally, the gate negative voltage is maintained to the potentialGateC during the blanking period in which the device functions as thetouch sensor, thereby increasing the amplitude of the common drivesignal Vcom supplied during the blanking period (increasing thepotential difference between the potential VcomA and the potentialVcomB), which improves the performance as the sensor.

Next, variation in potentials of negative polarity pixels will beexplained. Assume that Gate2 next to Gate 1 is a potential of the gateline 2 connected to the negative polarity pixels. In this case, thenegative polarity pixels connected to the gate line 2 are turned on whenthe potential GateA is switched to the potential GateB at a timing shownin FIG. 12, and writing is performed based on the video signal. Thepotential Vpix2 is maintained in the potential VpixB after the writingis performed.

When the vertical blanking period starts and the common drive signalVcom in which the potential VcomA and the potential VcomB are repeatedwith a given cycle is added while the potential Vpix2 of the liquidcrystal capacitor C is maintained in the potential VpixB, the potentialVpix2 of the liquid crystal capacitor C becomes a signal in which thepotential VpixA and the potential VpixB are repeated so as to correspondto the cycle. As the potential Vpix2 of the liquid crystal capacitor Cof the negative polarity pixels varies as described above, the potentialof Gate2 is returned and fixed to the potential GateA during the period.That is, the potential of Gate2 is returned to the potential GateA fromthe potential GateB and fixed to the potential GateA also during theblanking period as shown in FIG. 12.

In the case of the positive polarity, the switch 171 of the gate buffer161 (FIG. 11B) is connected to a terminal “b” at a point before thevertical blanking period, and the gate buffer 161 outputs a signal inthe potential GateA supplied through the VGL1 line. Then, in thevertical blanking period, the switch 171 is switched from the terminal“b” to the terminal “a”, and the gate buffer 161 outputs a signal in thepotential GateC supplied through the VGL2 line.

As described above, the negative supply with respect to the positivepolarity pixels is maintained in the potential GateC which is lower thanthe potential GateB used when turning on the TFT circuit 61 and higherthan the reference potential GateA during the vertical blanking period.The negative supply with respect to the negative polarity pixels isreturned to the reference potential GateA from the potential GateB usedwhen turning on the TFT circuit 61, and then, maintained in thepotential GateA during the vertical blanking period.

In the variation of potentials applied to gates of positive polaritypixels explained with reference to FIG. 12, the potential of thenegative supply is made to be higher during the vertical blankingperiod. It is also possible that the potential of the negative supply isincreased and reduced in synchronization with the common drive signalVcom instead of increasing the potential of the negative supply duringthe vertical blanking period. Timing charts in this case are shown inFIG. 13.

FIG. 13 shows timing charts for explaining variation of gate potentialsin the vertical blanking period. When comparing the timing charts shownin FIG. 13 with the timing charts shown in FIG. 12, a point that thegate potential of positive polarity pixels is synchronized with thecommon drive signal Vcom is different.

The common drive signal Vcom is a signal with a given cycle during thevertical blanking period, in which the potential VcomA and the potentialVcomB are repeated with a given cycle, sequentially supplied torespective pixels. When assuming that the Gate1 is the potential of thegate line 1 connected to the positive polarity pixels in the same manneras the case explained with reference to FIG. 12, the positive polaritypixels connected to the gate line 1 are turned on when the potentialGateA is switched to the potential GateB at a timing shown in FIG. 13,and writing is performed based on the video signal. The potential Vpix1is maintained in the potential VpixC after the writing is performed.

When the vertical blanking period starts and the common drive signalVcom in which the potential VcomA and the potential VcomB are cyclicallyrepeated is added while the potential Vpix1 of the liquid crystalcapacitor C is maintained in the potential VpixC, the potential Vpix1 ofthe liquid crystal capacitor C becomes a signal in which the potentialVpixC and the potential VpixD are repeated so as to correspond to thecycle. Then, the potential of Gate1 will be a signal in which thepotential GateA and the potential GateC are repeated.

As described above, the potential of Gate1 will be a signal in which thepotential GateA and the potential GateC are repeated in the same cycleas the cycle of the common drive signal Vcom during the blanking periodat the time of the positive polarity. In such case, for example, theswitch 171 of the gate buffer 161 (FIG. 11B) switches the connection tothe terminal “a” or the terminal “b” so as to correspond to the cycle ofthe common drive signal Vcom. The gate buffer 161 outputs the signal inthe potential GateA from the VGL1 line supplied through the terminal tobe connected or outputs the signal in the potential GateC from the VGL2line.

In the negative polarity pixels, the signal in which the potential isswitched to the potential GateB only when turning on the TFT circuit 61and is the potential GateA in other periods is supplied. Also in thiscase, the TFT circuits 61 of the negative polarity pixels are controlledso as not to exceed the withstand voltage.

[Gate Potential in Horizontal Blanking Period]

FIG. 14 shows timing charts for explaining variation of gate potentialsin a horizontal blanking period. A potential applied to gates of the TFTcircuits 61 of the positive polarity in synchronization with the givencycle of the common drive signal Vcom, for example, GateM will be asignal in which the potential GateA and the potential GateC are repeatedalso during the horizontal blanking period. When the timing of writingcomes during the period, the potential GateA is switched to thepotential GateB for turning on the TFT circuits 61.

As described above, at the time of the positive polarity, the gatepotential will be the signal in which the potential GateA and thepotential GateC are repeated in the same cycle as the cycle of thecommon drive signal Vcom during the horizontal blanking period andduring periods other than a period when the TFT circuits 61 is turnedon. At the time of negative polarity, the gate potential will be asignal in which the potential GateB is taken only when the TFT circuits61 are turned on and the potential GateA is taken in other periodsregardless of the horizontal blanking period.

The variation of the gate potentials in the horizontal blanking periodshown in FIG. 14 is the same in the case where the gate potential in thevertical blanking period shown in FIG. 12 becomes high during the periodwhen the device functions as the touch panel and in the case where thegate potential in the horizontal blanking period shown in FIG. 13becomes high in synchronization with the common drive signal Vcom.

As the signal supplied to the gates of positive polarity pixels is thesignal in synchronization with the common drive signal Vcom during theblanking period as described above, the potential of the negative supplyof the gates is also increased corresponding to the variation even whenthe potential Vpix1 of the liquid crystal capacitor C varies between thepotential VpixC and the potential VpixD as explained with reference toFIGS. 8A and 8B, therefore, the potential can be controlled withoutexceeding the withstand voltage of the TFT circuit 61. Additionally, thegate negative voltage is maintained in the potential GateC during theblanking period when the device functions as the touch sensor, therebyincreasing the amplitude of the common drive signal Vcom supplied duringthe blanking period (increasing the potential difference between thepotential VcomA and the potential VcomB), which can improve theperformance as the sensor.

[Case where Same Gate Signal is Used in Positive Polarity and NegativePolarity]

In the above embodiment, the case where different gate signals are usedfor the positive polarity and the negative polarity has been explainedas the example. It is possible to use the same gate signal for thepositive polarity and the negative polarity. As shown in FIG. 13 andFIG. 14, the gate potential becomes high in synchronization with thecommon drive signal Vcom during the vertical blanking period and thehorizontal blanking period also at the time of the negative polarity,thereby configuring the device so that the same gate signal is used forthe positive polarity and the negative polarity.

Timing charts in the case where the gate potential becomes high insynchronization with the common drive signal Vcom during the verticalblanking period also at the time of the negative polarity are shown inFIG. 15. In the timing charts shown in FIG. 15, timing charts concerningthe positive polarity are the same as the timing charts concerning thepositive polarity in the timing charts shown in FIG. 13, and thepotential of Gate1 will be a signal in which the potential GateA and thepotential GateC are repeated in the same cycle as the cycle of thecommon drive signal Vcom during the vertical blanking period.

Next, variation in potentials of negative polarity pixels will beexplained. The common drive signal Vcom is a signal with a given cycleduring the vertical blanking period, in which the potential VcomA andthe potential VcomB are repeated with a given cycle, sequentiallysupplied to respective pixels. When assuming that Gate2 is the potentialof the gate line 2 connected to the negative polarity pixels, thenegative polarity pixels connected to the gate line 2 are turned on whenthe potential GateA is switched to the potential GateB at a timing shownin FIG. 15, and writing is performed based on the video signal. Thepotential Vpix2 is maintained in the potential VpixA (FIG. 8A) after thewriting is performed.

When the vertical blanking period starts and the common drive signalVcom in which the potential VcomA and the potential VcomB are cyclicallyrepeated is added while the potential Vpix2 of the liquid crystalcapacitor C is maintained in the potential VpixA, the potential Vpix2 ofthe liquid crystal capacitor C becomes a signal in which the potentialVpixA and the potential VpixB (FIG. 8A) are repeated so as to correspondto the cycle. Then, the potential of Gate2 will be a signal in which thepotential GateA and the potential GateC are repeated.

As described above, the potential of Gate2 will be a signal in which thepotential GateA and the potential GateC are repeated in the same cycleas the cycle of the common drive signal Vcom during the blanking periodalso in the negative polarity in the same manner as the case of thepositive polarity. That is, as shown in FIG. 15, the same signal issupplied to positive polarity pixels and negative polarity pixels as thegate signal respectively regardless of the polarity.

In the case where the gate potential becomes high in synchronizationwith the common drive signal Vcom at the time of the negative polarity,timing charts will be as shown in FIG. 16 also in the horizontalblanking period. In the timing charts shown in FIG. 16, timing chartsconcerning the positive polarity are the same as the timing chartsconcerning the positive polarity in the timing charts shown in FIG. 14,therefore, the explanation thereof is omitted.

During the horizontal blanking period, a potential to be applied togates of TFT circuits 61 in the negative polarity in synchronizationwith the given cycle of the common drive signal Vcom, for example,GateM+1 will be a signal in which the potential GateA and the potentialGateC are repeated. When the timing of writing comes during the period,the potential GateA is switched to the potential GateB for turning onthe TFT circuits 61.

The above variation of potentials is the same as variation of the gatepotential with respect to the positive polarity. As described above, thepotential will be a signal in which the potential Gate A and thepotential GateC are repeated in the same cycle as the cycle of thecommon drive signal Vcom during periods other than the period whenturning on the TFT circuits 61 in the horizontal period also at the timeof the negative polarity in the same manner as the positive polarity.

The switch 171 of the gate buffer 161 (FIG. 11B) connected to targetpixels of the positive polarity and the negative polarity switches theconnection to the terminal “a” or the terminal “b” so as to correspondto the cycle of the common drive signal Vcom. The gate buffer 161outputs the signal in the potential GateA from the VLG1 line suppliedthrough the connected terminal or the signal in the potential GateC fromthe VGL2 line.

As the same signal is supplied to the positive polarity pixels and thenegative polarity pixels as the gate signal respectively regardless ofthe polarity, it is not necessary to allow the gate negative supply tobe independent for the negative polarity and the positive polarity,which is different from the case where different gate signals aresupplied for the positive polarity and for the negative polarity.Accordingly, the polarity arrangement pattern of pixels and theconnection pattern of gate lines can be the structure shown in FIG. 9A.FIG. 9A shows the case where the same gate signal is used for thenegative polarity and the positive polarity, which is the case where thepolarity arrangement pattern is the pattern called the dot inversiondrive.

It is not necessary to allow the gate negative supply to be independentfor the negative polarity and the positive polarity in the embodiment,however, it is also possible to apply the dot inversion drive as thepolarity arrangement pattern and the connection pattern in which thegate lines connect pixels of the same polarity as shown in FIG. 9B.Moreover, in the line inversion drive as shown in FIG. 10, theembodiment in which the same gate signal is supplied to pixels of thepositive polarity and the negative polarity can be applied.

As the gate signal which is synchronized with the amplitude of thecommon drive signal Vcom is supplied also at the time of the negativepolarity, the connection pattern of gate lines can be designed so as tocorrespond to the related-art connection pattern (the pattern shown inFIG. 9A) and to the related-art polarity arrangement pattern (patternsshown in FIG. 9B and FIG. 10).

Moreover, as the signal supplied to gates of pixels of the positivepolarity and the negative polarity is synchronized with the common drivesignal Vcom during the blanking period, the negative supply of the gatesbecomes high so as to correspond to variation of the potential Vpix1 ofthe liquid crystal capacitor C between the potential VpixC and thepotential VpixD, therefore, it is possible to control the circuit not toexceed the withstand voltage of the TFT circuit 61 of the pixel evenwhen the pixel is the positive polarity.

Furthermore, as the gate negative voltage is maintained in the potentialGateC during the blanking period when the device functions as the touchsensor, the amplitude of the common drive signal Vcom supplied duringthe blanking period can be increased (the potential difference betweenthe potential VcomA and the potential VcomB can be increased), whichimprove the performance as the sensor.

As explained with reference to the timing charts shown in FIG. 12, inthe case of applying the configuration in which the potential of thegate negative supply is maintained to be high with respect to thepositive polarity pixels, not being synchronized with the amplitude ofthe common drive signal Vcom during the vertical blanking period (duringthe period when functioning as the touch panel), it is not preferable toapply the configuration in which the potential of the gate negativesupply is maintained to be high also with respect to the negativepolarity pixels.

If the configuration in which the potential of the gate negative supplyis maintained to be high with respect to the negative polarity pixelduring the blanking period, there is a possibility that the potential ofnegative polarity pixels leaks. Accordingly, it is necessary toconfigure the device so that the potential of the negative polaritypixels does not leak, and it is not preferable to apply theconfiguration in which the potential of the gate negative supply ismaintained to be high during the blanking period.

Consequently, as explained with reference to FIG. 12, it is preferableto apply the configuration in which the potential of the gate negativesupply is maintained to be high with respect to the positive polaritypixels during the blanking period and the potential of the gate negativesupply is not maintained to be high with respect to the negativepolarity pixels during the blanking period. In other words, it ispreferable that the gate negative supply is allowed to be independentfor the negative polarity and the positive polarity and that thepotential of the gate negative supply is increased only with respect tothe positive polarity pixels.

[Advantages]

As described above, according to the embodiment of the presentdisclosure, it is possible to prevent the voltage of the TFT circuits toexceed the withstand voltage by increasing the potential of the gatenegative supply with respect to the positive polarity pixels when thedisplay device with the touch sensor functions as the touch sensor. Asthe potential of the gate negative supply is increased, the potential ofthe common drive signal Vcom can be increased accordingly (more than theincrease by the gate negative supply) to be applied to the TFT circuits.Accordingly, it is possible to increase the amplitude of the commondrive signal Vcom and to thereby increase the performance as the touchsensor.

Moreover, as the period during which the potential of the gate negativesupply is increased is provided in the vertical blanking period or thehorizontal blanking period which is not the writing period with respectto pixels, it is possible to prevent occurrence of leakage due to imagedata.

Furthermore, the potential of the gate negative supply is increased,thereby reducing the difference between “a potential difference Vpix+between a potential Vpix+ of positive polarity pixels and a potentialVGate of Gate” and “a potential difference Vpix− between a potentialVpix− of negative polarity pixels and a potential VGate of Gate”. Thedifference of leakage amounts of potentials between the positivepolarity and the negative polarity can be reduced by reducing the abovedifference. As a result, it is possible to suppress flicker and toincrease the image quality.

[Recording Media]

The above series of processing can be executed by hardware as well assoftware. When the series of processing is executed by software,programs included in the software are installed to a computer. Here, thecomputer includes a computer incorporated in dedicated hardware, ageneral-purpose personal computer capable of executing various functionsby installing various programs and so on.

FIG. 17 is a block diagram showing a configuration example of hardwareof the computer executing the above series of processing by a program.In the computer, a CPU (Central Processing Unit) 301, a ROM (Read OnlyMemory) 302, a RAM (Random Access Memory) 303 are mutually connected bya bus 304. An input/output interface 305 is further connected to the bus304. An input unit 306, an output unit 307, a storage unit 308, acommunication unit 309 and a drive 310 are connected to the input/outputinterface 305.

The input unit 306 includes a keyboard, a mouse, a microphone and so on.The output unit 307 includes a display, a speaker and so on. The storageunit 308 includes a hard disk, a nonvolatile memory and so on. Thecommunication unit 309 includes a network interface and so on. The drive310 drives removable media 311 such as a magnetic disc, an optical disc,a magneto-optical disc and a semiconductor memory.

In the computer configured as the above, the CPU 301 loads the programstored in, for example, the storage unit 308 to the RAM 303 through theinput/output interface 305 and the bus 304 and executes the program,thereby performing the above series of processing.

The program executed by the computer (CPU 301) can be provided byrecording the program in the removable media 311 such as package media.The program can be provided through wired or wireless transmission mediasuch as a local area network, Internet and digital satellitebroadcasting.

In the computer, program can be installed in the storage media 308through the input/output interface 305 by mounting the removable media311 on the drive 310. The program can be also installed in the storage308 by receiving by the communication unit 309 through wired or wirelesstransmission media. The program can be also installed in advance in theROM 302 or the storage 308.

The program executed by the computer may be a program in whichprocessing is performed in time series along the order explained in thepresent specification as well as a program in which processing isperformed in parallel or at a necessary timing such as calling isperformed.

In the present specification, the system indicates the entire deviceincluding plural devices.

The embodiment of the present disclosure is not limited to the aboveembodiment but various modifications can be made within a scope notdeparting from the gist of the present disclosure.

The present disclosure may be configured as the following structures.

(1) A display device with a touch sensor including

plural display pixel electrodes,

a common electrode arranged opposite to the display pixel electrodes,

a display function layer having an image display function,

a display control circuit performing image display control so as tofulfill the display function of the display function layer by applying avoltage for display between the display pixel electrodes and the commonelectrode based on an image signal, and

a touch detection electrode provided opposite to the common electrodeand forming capacitance between the touch detection electrode and thecommon electrode,

in which a drive voltage for display applied to the common electrode bythe display control circuit is used as a drive signal for the touchsensor, and

a gate potential of TFT circuits included in the display pixelelectrodes is increased during a period when the drive signal for thetouch sensor is applied.

(2) The display device with the touch sensor described in the above (1),

in which the gate potential is in a high state during a verticalblanking period and a horizontal blanking period.

(3) The display device with the touch sensor described in the above (2),

in which the gate potential becomes in the high state in synchronizedwith the drive signal for the touch sensor.

(4) The display device with the touch sensor described in any of theabove (1) to (3),

in which the gate potential becomes in a high state when writing in apositive polarity display voltage is performed.

(5) A potential control method of a display device with a touch sensorincluding

plural display pixel electrodes,

a common electrode arranged opposite to the display pixel electrodes,

a display function layer having an image display function,

a display control circuit performing image display control so as tofulfill the display function of the display function layer by applying avoltage for display between the display pixel electrodes and the commonelectrode based on an image signal, and

a touch detection electrode provided opposite to the common electrodeand forming capacitance between the touch detection electrode and thecommon electrode, the method including

using a drive voltage for display applied to the common electrode by thedisplay control circuit as a drive signal for the touch sensor, and

increasing a gate potential of TFT circuits included in the displaypixel electrodes is increased during a period when the drive signal forthe touch sensor is applied.

(6) A program for a computer controlling a display device with a touchsensor including

plural display pixel electrodes,

a common electrode arranged opposite to the display pixel electrodes,

a display function layer having an image display function,

a display control circuit performing image display control so as tofulfill the display function of the display function layer by applying avoltage for display between the display pixel electrodes and the commonelectrode based on an image signal, and

a touch detection electrode provided opposite to the common electrodeand forming capacitance between the touch detection electrode and thecommon electrode, the program allowing the computer to executeprocessing of

using a drive voltage for display applied to the common electrode by thedisplay control circuit as a drive signal for the touch sensor, and

increasing a gate potential of TFT circuits included in the displaypixel electrodes is increased during a period when the drive signal forthe touch sensor is applied.

(7) A display device with a touch sensor including

plural display pixel electrodes,

a common electrode arranged opposite to the display pixel electrodes,

a display function layer having an image display function,

a display control circuit performing image display control so as tofulfill the display function of the display function layer by applying avoltage for display between the display pixel electrodes and the commonelectrode based on an image signal, and

a touch detection electrode provided opposite to the common electrodeand forming capacitance between the touch detection electrode and thecommon electrode,

in which a drive voltage for display applied to the common electrode bythe display control circuit is used as a drive signal for the touchsensor, and

a signal supplied to gates of TFT circuits included in the display pixelelectrodes is a signal in which different three potentials are switchedat given timings.

(8) The display device with the touch sensor described in the above (7),

in which the three potentials includes a first potential to be areference, a second potential for turning on the TFT circuits and athird potential at the time of supplying the drive signal for the touchsensor.

(9) The display device with the touch sensor described in the above (8),

in which a potential of the signal supplied to gates of the TFT circuitsin a vertical blanking period and in a horizontal blanking period is thethird potential.

(10) The display device with the touch sensor described in any of theabove (7) to (9),

in which the signal supplied to gates of the TFT circuits is a signalsynchronized with the drive signal for the touch sensor, in which thefirst potential and the third potential are repeated.

(11) The display device with the touch sensor described in any of theabove (7) to (10),

in which the signal supplied to gates of the TFT circuits is a signal inwhich different three potentials are switched at given timings whenwriting in a positive polarity display voltage is performed, and is asignal in which two potentials of the different three potentials areswitched at given timings when writing in a negative polarity displayvoltage is performed.

(12) A potential control method of a display device with a touch sensorincluding

plural display pixel electrodes,

a common electrode arranged opposite to the display pixel electrodes,

a display function layer having an image display function,

a display control circuit performing image display control so as tofulfill the display function of the display function layer by applying avoltage for display between the display pixel electrodes and the commonelectrode based on an image signal, and

a touch detection electrode provided opposite to the common electrodeand forming capacitance between the touch detection electrode and thecommon electrode, the method including

using a drive voltage for display applied to the common electrode by thedisplay control circuit as a drive signal for the touch sensor, and

allowing a signal supplied to gates of TFT circuits included in thedisplay pixel electrodes to be a signal in which different threepotentials are switched at given timings.

(13) A program for a computer controlling a display device with a touchsensor including

plural display pixel electrodes,

a common electrode arranged opposite to the display pixel electrodes,

a display function layer having an image display function,

a display control circuit performing image display control so as tofulfill the display function of the display function layer by applying avoltage for display between the display pixel electrodes and the commonelectrode based on an image signal, and

a touch detection electrode provided opposite to the common electrodeand forming capacitance between the touch detection electrode and thecommon electrode, the program allowing the computer to executeprocessing of

using a drive voltage for display applied to the common electrode by thedisplay control circuit as a drive signal for the touch sensor, and

allowing a signal supplied to gates of TFT circuits included in thedisplay pixel electrodes to be a signal in which different threepotentials are switched at given timings.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The invention is claimed as follows:
 1. A display device with a touch sensor comprising: a plurality of pixel electrodes having TFT circuits; a common electrode arranged opposite to the pixel electrodes; a display function layer having an image display function; a display control circuit performing image display control so as to fulfill the display function of the display function layer by applying a voltage for display between the pixel electrodes and the common electrode based on an image signal; a gate buffer coupled with gates of the TFT circuits through each of gate lines, the gate buffer being switched to be coupled with one of a first-L line and a first-H line through a first switch; and a second line, wherein a drive voltage for display applied to the common electrode by the display control circuit is used as a drive signal for the touch sensor, wherein a signal supplied to the gates of the TFT circuits is one of a pulse wave signal and a signal in which different three potentials are switched at given timings, wherein the three potentials include a first potential supplied through the first-L line, a second potential supplied through the second line, and a third potential supplied through first-H line, and wherein the first switch switches to couple the gate buffer with the first-L line and the first-H line in synchronization with the drive signal in which a first common potential and a second common potential are repeated, such that the gates of the TFT circuits are supplied with the pulse wave signal in which the first potential and the third potential are repeated, the third potential being greater than the first potential and less than the second potential.
 2. The display device with the touch sensor according to claim 1, wherein the first potential is supplied during the TFT circuits being off, the second potential is supplied for turning on the TFT circuits, and the third potential is supplied at the time of supplying the drive signal for the touch sensor.
 3. The display device with the touch sensor according to claim 1, wherein a potential of the signal supplied to the gates of the TFT circuits in a vertical blanking period and in a horizontal blanking period is the third potential, and the third potential is higher than the first potential.
 4. The display device with the touch sensor according to claim 1, wherein the signal supplied to the gates of the TFT circuits is the signal in which different three potentials including the first potential, and the second potential, and the third potential are switched at given timings when writing in a positive polarity display voltage is performed, and is a signal in which the first potential and the second potential are switched at given timings when writing in a negative polarity display voltage is performed. 